Gas turbine engines are used to power aircraft, watercraft, power generators, and other vehicles and machines. Gas turbine engines typically include one or more compressors, a combustor, and one or more turbines. In typical aerospace applications, a fan or propeller is used to draw air into the engine and feeds the drawn-in air to the gas turbine core, which includes one or more compressors, a combustor, and one or more turbines. The compressor includes alternating stages of rotors (e.g., rotating disks with blades) and stators (e.g., static vanes), which increase the pressure of the drawn-in air as it travels through the gas turbine core. The compressor thus outputs higher-pressure air, which it delivers to the combustor. In the combustor, the fuel is mixed with the higher-pressure air and is ignited by an igniter. The products of the combustion reaction that occurs in the combustor (e.g., hot gas) are directed into a turbine. The turbine is typically made up of an assembly of rotors (e.g., rotating discs with blades), which are attached to turbine shafts, nozzle guide vanes, casings, and other structures. The turbine converts the thermal energy supplied by the combustion products into kinetic energy. The work extracted from the combustion products by the turbine may be used to drive the fan, the compressor, and, sometimes, an output shaft. Leftover products of the combustion are exhausted out of the engine and may provide thrust in some configurations.
Aerospace applications of gas turbine engines include turboshaft, turboprop, and turbofan engines. In typical aerospace applications, the gas turbine engine provides thrust to propel the aircraft, and also supplies power for engine accessories and aircraft accessories. Mechanical power is transferred from turbines to compressors through shaft and spline systems, with bearings providing axial and radial positioning of the rotating components. A drive shaft typically links the turbine and compressor sections of the turbine engine. In turbine engines having multiple turbine and compressor sections, there may be multiple, concentric, independently rotatable drive shafts. For example, a high pressure shaft may link a high pressure compressor with a high pressure turbine, while a low pressure shaft links the fan with a low pressure turbine. The low pressure shaft may be concentric with and disposed within the high pressure shaft.